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Mimas is a moon of Saturn that was discovered in 1789 by William Herschel. It is named after Mimas, a son of Gaia in Greek mythology, and is also designated Saturn I.


Mimas was one of the Titans of Greek mythology. The name "Mimas", indeed the names of all seven then-known satellites of Saturn, were suggested by Herschel's son John Herschel in his 1847 publication Results of Astronomical Observations made at the Cape of Good Hope [1]. He named them after Titans specifically because Saturn, known as Kronos in Greek mythology, was the leader of the Titans.

According to Liddell and Scott's A Greek-English Lexicon, the adjectival form of Mimas/Mimans would be Mimantean (the genitive case is Mimantis, Greek Μῑμάντις). In practice, anglicisms such as Mimasian and Mimian are very occasionally seen, but more commonly writers simply use the phrase 'of Mimas'.

Physical characteristics

Mimas' low density (1.17) indicates that it is composed mostly of water ice with only a small amount of rock. Due to the tidal forces acting on it, the moon is not perfectly spherical; its longest axis is about 10% longer than the shortest. The somewhat ovoid shape of Mimas is especially noticeable in recent images from the Cassini probe.

Mimas' most distinctive feature is a colossal impact crater 130 km across, named Herschel after the moon's discoverer. Herschel's diameter is almost a third of the moon's own diameter; its walls are approximately 5 km high, parts of its floor measure 10 km deep, and its central peak rises 6 km above the crater floor. If there were a crater of an equivalent scale on Earth it would be over 4,000 km in diameter, wider than Canada. The impact that made this crater must have nearly shattered Mimas: fractures can be seen on the opposite side of Mimas that may have been created by shock waves from the impact travelling through the moon's body.

The surface is saturated with smaller impact craters, but no others are anywhere near the size of Herschel. Although Mimas is heavily cratered, the cratering is not uniform. Most of the surface is covered with craters greater than 40 km in diameter, but in the south polar region, craters greater than 20 km are generally lacking. This suggests that some process removed the larger craters from these areas.

Scientists officially recognise two types of geological features on Mimas: craters and chasmata (chasms). See also: List of geological features on Mimas.

Mimas is responsible for clearing the material from the Cassini Division, the gap between Saturn's two widest rings, A Ring and B Ring. Particles at the inner edge of the Cassini division are in a 1:2 resonance with the moon called Mimas. They orbit twice for every one orbit of Mimas. The repeated pulls by Mimas on the Cassini division particles, always in the same direction in space, force them into new orbits outside the gap. Other resonances with Mimas are also responsible for other features in Saturn's rings: the boundary between the C and B ring is at the 1:3 resonance and the outer edge of the A ring is at the 2:3 resonance.

External links


(Saturn's natural satellite navigator) | Mimas | Enceladus | ...

Saturn (satellites)
Janus' group | Mimas | Enceladus | Tethys | Dione | Rhea | Titan | Hyperion | Iapetus | Inuit group | Gallic group | Norse group
See also: Pronunciation key | Rings of Saturn

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